An air bag is inflated to help protect an occupant of a vehicle upon occurrence of a vehicle collision. When the vehicle experiences a collision-indicating condition of at least a predetermined threshold level, an igniter is actuated so as to ignite a gas generating material. As the generating material burns, it generates a volume of inflation gas. The inflation gas is directed into the air bag to inflate the air bag. When the air bag is inflated, it expands into the vehicle occupant compartment and helps to protect the vehicle occupant.
Another apparatus that protects an occupant of a vehicle upon the occurrence of a vehicle collision is a seat belt associated with a seat belt pretensioner. The pretensioner can be actuated by a gas provided by a gas generator. When the vehicle experiences a collision indicating-condition for which pretensioning of the seat belt is desired, an igniter is actuated so as to ignite a gas generating material. As the generating material burns, it generates a volume of gas. The gas is directed against a mechanism, e.g., a piston, connected to a cable. The seat belt is then tightened against the vehicle occupant.
It is known to use an energetic cellulose, such as nitrocellulose (NC), as a gas generating material in an vehicle occupant protection apparatus. One limitation to using nitrocellulose as a gas generating material in a vehicle occupant protection apparatus is that nitrocellulose decomposes over time.
A stabilizer can be combined with nitrocellulose to retard the decomposition of nitrocellulose at ambient temperatures (i.e., about 25° C.). A commonly used stabilizer is diphenylamine (DPA). Diphenylamine is used in a nitrocellulose gas generating material at levels below about 0.7% by weight of the gas generating material. This level is not effective to retard the decomposition of nitrocellulose when nitrocellulose is exposed to elevated temperatures (i.e., above about 65° C.). Further, simply increasing the level of stabilizer combined with nitrocellulose does not retard the decomposition of nitrocellulose. Higher levels of diphenylamine seem to accelerate the decomposition of nitrocellulose. The accelerated decomposition of stabilized nitrocellulose at elevated temperatures appears to be caused by the basic and/or nucleophilic properties of diphenylamine.